Dynamics of radioiodine accumulation on soil and reconstraction of doses from iodine exposure on the territory contaminated after the Chernobyl accident

The paper presents distributions of external doses and absorbed doses from thyroid internal exposure on the territory of the former USSR due to exposure of 131I and 132I released into the environment as a result of the Chernobyl accident. Dose assessments were based on measurements of daily depositions of 131I and 132Te from the atmosphere made by SPA Typhoon. The main body of available measurement data were added with calculations of 131I depositions from space-time correlations and results of measurements of total p-activity, 137Cs etc. Based on these data calculations were made of 131I and 132I accumulation on soil surface, exposure dose rate and exposure dose from y-irradiation 131I and 132I from the soil surface, and absorbed thyroid doses from incorporated 131I and 132I. Estimated errors in calculations are also presented. Besides, the paper includes ganerated maps of 131I contamination of the soil by 15 May 1986 and distribution of external and internal thyroid exposure doses from incorporated 131I and 132I accumulated by 1 september 1986. The dominant radiation load from 131I and 132I has been shown to be due to internal thyroid rxposure to incorporated 131I. Given no iodine prophylaxis and restrictions in the diet of the residents, it could have been three orders of magnitude higher the external exposure doses. In different points of the former USSR, the maximum contamination was reported on different dates from 28 April to 3 May 1986. By estimation, of the major cities the highest radiation loads due to 131I occired in Gomel where by 1 June the exposure dose was 134 mR and the thyroid exposure dose was 166 cSv. The highest radiation loads from 132Te + 132I were in Kiev where by 1 June 1986 the thyroid exposure dose was 720 |xSv (72 mrem) and the exposure dose - 965 mR.